Suction

Child (age 3): Knock knock

Parent: Who is there

Child: Tinkertoy has a suction-cup but can't stick to and arm pit or a body!!!!

Child: HAHAHAHAHAHAHA I am SOOOO funny

Child: DADDY! Watch! But these CAN stick to wood. They can't stick to wall. I will get down under the bed and get it.

(child jumps off bed with a clunk)

Child: I'm OK!!!!

Child: Daddy, I'm so funny, I said "I'MMM OK!!!!"

(even bigger jump off bed with bigger bonk on ground)

Child: See I did it again, I'm ok! I'm funny dad!

Child: What's the big idea dude? Dad, DAD! Watch it! Now I stick these together. Now I stick it to you and MAKE it stick on your body!!!!!!!